JP2020171944A - Pouring device for continuous casting - Google Patents

Abstract

To provide a pouring device for continuous casting capable, in continuous casting using a single-holed immersion nozzle having a single discharge hole at a lower end of the immersion nozzle, of imparting a rotational flow to a molten metal flowing down an interior of the immersion nozzle without shortening the lifetime of the immersion nozzle or a sliding gate.SOLUTION: A pouring device for continuous casting has a sliding gate 1 having a passage-axis inclination angle α of 5° or greater and 75° or smaller between a passage-axis direction and a slide-face vertically downstream direction of flow passage holes 6 in respective plates 2 and a slide-face passage-axis direction different between the plates and changing clockwise or counterclockwise as going downstream, thereby forming a rotational flow of molten steel. An immersion nozzle 11 is made up with a single discharge hole made open in a bottom portion of the immersion nozzle.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pouring device for continuous casting.

In the continuous casting of molten metal, for example, molten steel, the molten steel contained in the ladle is transferred to the tundish and further injected from the tundish into the mold. A flow rate adjusting mechanism such as a sliding gate is provided at the bottom of the tundish, a dipping nozzle is provided on the downstream side of the sliding gate, and a discharge hole for discharging molten steel into the mold is provided on the side near the lower end of the dipping nozzle. There is.

In large-section bloom continuous casting and slab continuous casting, a two-hole discharge hole is provided on the side surface of the immersion nozzle, and the discharge holes are usually provided on both sides in the width direction of the mold (width direction of the slab). On the other hand, in small-section bloom continuous casting and billet continuous casting, a single-hole discharge hole facing downward is provided at the lower end of the immersion nozzle. Hereinafter, it is also referred to as a “single-hole immersion nozzle”. The present invention targets a hot water pouring device for continuous casting, which uses a single-hole dipping nozzle as the discharge hole shape of the dipping nozzle.

In continuous casting using a single-hole immersion nozzle, the discharge flow penetrates deeply into the strands and the surface temperature of the molten steel in the mold tends to drop, and the molten metal surface begins to peel and captures floating bubbles and inclusions. It will be easier. As a result, it is known that problems such as deterioration of quality of the central portion and the surface layer portion of the slab and poor slagging of the mold powder occur (see Non-Patent Document 1). In addition, it leads to operational problems such as breakout and damage to the immersion nozzle.

In Patent Document 1, a dipping nozzle for continuous casting, which is used in a continuous casting method for steel, is referred to as a "swirl flow nozzle" by installing a torsion plate type swivel blade inside to apply a swirling flow to the molten steel flowing down the nozzle. We call it and disclose a continuous casting method using this swirling flow nozzle.
According to Patent Document 1, when a swirling flow nozzle is applied in the case of a single-hole immersion nozzle having one discharge hole at the bottom of the tubular nozzle, the discharge flow is expanded while being discharged by centrifugal force, so that the discharge flow velocity is reduced. An electromagnetic braking effect is obtained in which the depth at which the discharge flow penetrates into the slab is reduced. Due to this effect, the floating of inclusions in the mold is promoted (for example, Non-Patent Document 2), the temperature of the hot water surface (meniscus) in the mold rises, the melt slag of the mold powder is promoted, and the slab surface is improved. It is expected that the temperature inside the slab will decrease, equiaxed crystals will increase, and porosity defects in the center of the slab will decrease.
Further, according to Patent Document 1, as a result of using a single-hole immersion nozzle having a tubular cross section extending from the inner wall of the nozzle hole toward the discharge hole and using a swirling flow nozzle, the molten steel flowing down while swirling is caused by centrifugal force. Since the discharge is performed while spreading laterally, non-metal inclusions are brought deep into the slab due to the discharge flow, and the molten steel supply to the molten steel surface (meniscus) in the mold is insufficient and the temperature drops, causing bubbles and non-metal inclusions. Problems such as hindering levitation separation are resolved. Further, since the stagnation area of the molten steel flow in the vicinity of the discharge hole is reduced, the adhesion of inclusions to the discharge hole is also reduced. Since the molten steel that flows down while swirling is discharged while spreading laterally due to centrifugal force, an ascending flow to the molten metal surface (meniscus) in the mold occurs, the molten metal surface temperature rises, and the floating separation of bubbles and non-metal inclusions is promoted. The effect of being done is obtained.

Patent Document 2 discloses a method of applying a swirling flow into the immersion nozzle by devising the shape of the intermediate nozzle in the process of injecting from the tundish into the mold. Is complicated and difficult to manufacture. Further, Patent Document 3 discloses a method of turning the molten steel by providing a notch in the flow path of the sliding gate, but this method can be obtained by giving a limited turn to the flow near the wall surface. The turning effect cannot be maintained because the turning is weak and the grooves and notches are melted.

In Patent Document 1, in a swirling flow nozzle in which a torsion plate type swirl vane is installed inside the nozzle, the swirl vane twist pitch Pc, the swirl vane twist angle θ, the outer diameter of the swirl vane, and the thickness of the swirl vane are defined within a predetermined range. Then, a method of continuously casting using a swirling flow nozzle in which the inner diameter is narrowed between the lower end of the swirling blade and the discharge hole and the required head predicted value H between the tundish and the mold is kept within a predetermined range is disclosed. Has been done.

JP-A-2002-239690 Japanese Unexamined Patent Publication No. 07-303949 Japanese Unexamined Patent Publication No. 2001-129646

"Swirl flow immersion nozzle for continuous casting of round billet" by Yuichi Tsukaguchi et al. Iron and Steel Vol. 93 (2007) No. 9, pp575-582 A. Vaterlaus et al, 3rd Conf. On CC (1998), 715

As described in Patent Document 1, by installing a twist plate type swivel blade in the dipping nozzle, a swirling flow is formed in the molten metal flow flowing down in the dipping nozzle, and then continuous casting using the single-hole dipping nozzle is performed. By doing so, the molten steel that flows down while swirling is discharged while spreading laterally due to centrifugal force, so that an ascending flow to the molten metal surface (meniscus) in the mold occurs and the molten metal surface temperature rises, causing bubbles and non-metal inclusions. Floating separation is promoted.
In addition, the rise in the temperature of the molten metal can be expected to suppress the skin contact of the molten metal.
On the other hand, there is a problem that the twisted plate type swivel blade provided in the immersion nozzle is easily melted and the effect is not maintained. If the immersion nozzle is replaced when the swirl blade is melted, there arises a problem that the life of the immersion nozzle is shortened.

An object of the present invention is to provide a continuous casting pouring device capable of imparting a swirling flow to a molten metal flow flowing down in a dipping nozzle without shortening the life of the dipping nozzle or the sliding gate.

That is, the gist of the present invention is as follows.
[1] A pouring device for continuous casting for pouring molten metal into a mold.
It has a sliding gate for adjusting the flow rate of the molten metal and a dipping nozzle provided below the sliding gate.
The sliding gate has a plurality of plates having flow path holes through which molten metal passes, and at least one of the plates is a slidable slide plate.
The flow path holes in each plate form an upstream surface opening on the upstream surface located on the upstream side of the molten metal passing through the surface of the plate, and a downstream surface on the downstream surface located on the downstream side. A hole is formed, and the direction from the center of gravity of the upstream surface opening figure to the center of gravity of the downstream surface opening figure is defined as the flow path axis direction.
The flow path axis inclination angle α formed by the downstream direction perpendicular to the sliding surface of the plate (hereinafter referred to as “sliding surface vertical downstream direction”) and the flow path axis direction is 5 ° or more and 75 ° or less.
The direction in which the flow path axis direction is projected onto the sliding surface is called the sliding surface flow path axis direction, and the direction in which the slide plate is slid when the sliding gate is closed is called the sliding closing direction. The angle formed by the sliding surface flow path axis direction clockwise with respect to the closing direction when viewed in the direction perpendicular to and downstream of the sliding surface is called the flow path axis rotation angle θ (range of ± 180 degrees), and the flow path is said to be The axis rotation angle θ differs between adjacent plates, with θ ₁ for the most upstream plate, θ _{2 for} the one downstream plate, and θ for the one downstream plate θ. _When numbered in order of ₃ and Δθ _N = θ _N −θ _{N + 1} (N is an integer of 1 or more and the number of plates is -1)
Both angles Δθ _N are greater than or equal to 10 ° and less than 170 ° to form a counterclockwise swirling flow in the immersion nozzle, or angles Δθ _N are both greater than −170 ° and less than −10 ° and the immersion nozzle. Forming a clockwise swirling flow inside,
The immersion nozzle is a hot water pouring device for continuous casting, characterized in that it has a single discharge hole opened at the bottom of the immersion nozzle.
[2] The pouring apparatus for continuous casting according to [1], wherein the discharge hole shape of the immersion nozzle is formed so as to have an expanding tubular shape from the inner wall of the immersion nozzle toward the discharge hole outlet. ..
[3] The pouring apparatus for continuous casting according to [1] or [2], wherein the number of plates forming the sliding gate is two or three, and the number of slide plates is one.

By using the present invention as a continuous casting pouring device for pouring molten metal into a mold, the life of the dipping nozzle and sliding gate is not shortened when performing continuous casting using a single-hole dipping nozzle. , Forming a swirling flow in the molten metal flow flowing down the immersion nozzle, forming an ascending flow to the molten metal surface (meniscus) in the mold, raising the molten metal surface temperature, and promoting the floating separation of bubbles and non-metal inclusions. Can be done.

It is a conceptual cross-sectional view which shows the pouring apparatus for continuous casting of this invention. It is a figure which shows the sliding gate of the pouring apparatus for continuous casting of this invention, (A) is a plan view of the upper fixing plate, (B) is a slide plate, (C) is a plan view of the lower fixing plate, (D) is a sliding A front view of the combination of the gate and the immersion nozzle, (E) is an arrow view of EE, and (F) is a cross-sectional view of the arrow FF. It is a figure which shows the sliding gate of the pouring apparatus for continuous casting of this invention, (A) is the arrow view of AA, (B) is the view of arrow BB, (C) is the view of arrow CC. , (D) is a front view of the combination of the sliding gate and the immersion nozzle, and (E) is an arrow view of EE. It is a figure which shows the flow in the sliding gate of this invention, (A) is the arrow view of AA, (B) is the view of arrow BB, (C) is the view of arrow CC, (D). Is a front view of the combination of the sliding gate and the immersion nozzle, and (E) is an arrow view of EE. It is a figure which shows the sliding gate of the pouring apparatus for continuous casting of this invention, (A) is the upper fixing plate, (B) is a slide plate, (C) is the front view which combined the sliding gate and the immersion nozzle, (D ) Is a view taken along the line DD, and (E) is a cross-sectional view taken along the line EE. It is a figure which shows the sliding gate of the pouring apparatus for continuous casting of this invention, (A) is the arrow view of AA, (B) is the view of arrow BB, (C) is the sliding gate and the immersion nozzle. The combined front view, (D) is a DD arrow view. It is a figure which shows an example of the upper fixing plate of this invention, (A) is a plan view, (B) is a front view, (C) is a side view, (D) is a cross-sectional view taken along the line DD. It is a figure which shows the sliding gate of the comparative example, (A) is an upper fixing plate, (B) is a slide plate, (C) is a front view which combined the sliding gate and a dipping nozzle, (D) is a DD arrow view. FIG. 3 (E) is a cross-sectional view taken along the line EE. It is a figure which shows the sliding gate of the comparative example, (A) is the arrow view of AA, (B) is the view of arrow BB, (C) is the front view which combined the sliding gate and the immersion nozzle, (D). ) Is a view taken along the line DD. It is a figure which shows the conventional sliding gate, (A) is a plan view of the upper fixing plate, (B) is a slide plate, (C) is a plan view of the lower fixing plate, and (D) is a front surface which combined the sliding gate and the immersion nozzle. The figure, (E) is an EE arrow view, and (F) is an FF arrow cross-sectional view. It is a figure which shows the conventional sliding gate, (A) is the arrow view of AA, (B) is the view of arrow BB, (C) is the view of arrow CC, (D) is the sliding gate. The front view in which the immersion nozzle is combined, (E) is an arrow view of EE. It is sectional drawing which shows the shape of the discharge hole in the immersion nozzle of the pouring apparatus for continuous casting of this invention. It is sectional drawing which shows the streamline of the discharge flow from the tip of a discharge hole. FIG.

As shown in FIG. 1, the present invention is a continuous casting pouring device 20 for pouring molten metal into a mold 22, and the sliding gate 1 for adjusting the flow rate of the molten metal and the sliding gate 1 It has an immersion nozzle 11 provided below. A swirling flow is formed at the sliding gate 1, and the molten metal flows down while swirling through the immersion nozzle inner hole 12. The immersion nozzle 11 has a discharge hole 13 opened downward at the bottom thereof, and the molten metal flowing down the immersion nozzle inner hole 12 is discharged from the discharge hole 13 while forming a swirling flow, and FIG. 13A ), The discharge flow 19 spreads concentrically from the end of the central shaft of the immersion nozzle with respect to the casting direction and the horizontal direction in the mold, and makes it possible to discharge.

《Sliding Gate》
First, the sliding gate of the present invention will be described with reference to FIGS. 1 to 11.
The sliding gate 1 is used for the purpose of adjusting the flow rate of the molten metal 23 in the process of injecting the molten metal 23 from the tundish 21 into the mold 22 in the continuous casting of the molten metal such as steel. In the sliding gate 1 formed by stacking two or three plates 2, each plate 2 is provided with a flow path hole 6. When the slide plate 4 of the plates constituting the sliding gate 1 is slid and the sliding gate 1 is "open" due to the overlap of the flow path holes 6 of the respective plates, the sliding gate 1 is opened from the upstream side to the downstream side of the flow path hole 6. The molten metal circulates toward the side. The direction perpendicular to the sliding surface 30 of the plate 2 toward the downstream direction (vertical downstream direction 32 of the sliding surface) is vertically downward from the top to the bottom.

In the conventionally used sliding gate, as shown in FIGS. 10 and 11, the flow path hole 6 of the plate 2 usually has a cylindrical inner peripheral shape, and the axial direction of the cylinder is perpendicular to and downstream of the sliding surface. It is configured to be parallel to the direction 32. On the other hand, in the present invention, as shown in FIGS. 2 to 9, the direction in which the flow path hole 6 faces is an oblique hole having an angle from the vertical downstream direction 32 of the sliding surface, and is projected onto the sliding surface 30. By appropriately combining two or three plates with different directions of the oblique holes, the molten metal flow inside the sliding gate 1 and the immersion nozzle 11 on the downstream side thereof can be changed only to the downstream side. Instead, a circumferential flow velocity is added to form a swirling flow.

As the cross-sectional shape of the flow path hole 6, a cylindrical shape having a perfectly circular cross section perpendicular to the axial direction is usually used. In the sliding gate 1 of the present invention, the flow path hole 6 formed in the plate 2 is not limited to a cylindrical shape, and the axial direction of the flow path hole may also change in the plate. Absent. Therefore, first, the axis of the flow path hole 6 formed in the plate 2 is defined.

The flow path hole 6 of the conventional sliding gate 1 will be described with reference to FIG. The sliding gate 1 of FIG. 10 has three plates 2 and is composed of an upper fixing plate 3, a slide plate 4, and a lower fixing plate 5 from the upstream side. Each plate 2 has a cylindrical shape with a perfect circular cross section, and a flow path hole 6 is formed in which the axial direction of the cylinder is perpendicular to the sliding surface 30 in the downstream direction (32 in the vertical downstream direction of the sliding surface). There is. The upstream surface of each plate is referred to as an upstream surface 7u, and the downstream surface is referred to as a downstream surface 7d. The figure (upstream surface opening) formed by the inner peripheral surface of the flow path hole 6 on the upstream surface 7u is called an upstream opening 8u. Further, a figure (downstream surface opening) formed on the downstream surface 7d by the inner peripheral surface of the flow path hole 6 is referred to as a downstream opening 8d. In the example shown in FIG. 10, since the cylindrical axis of the flow path hole 6 is perpendicular to the sliding surface, the upstream opening 8u and the downstream opening 8d overlap in FIGS. 10A to 10C. .. If the shapes of the upstream opening 8u and the downstream opening 8d are regarded as figures, the center of gravity of the figure can be defined. The center of gravity of the upstream surface opening figure is referred to as the upstream opening center of gravity 9u, and the center of gravity of the downstream surface opening graphic is referred to as the downstream opening center of gravity 9d. In the example shown in FIG. 10, since the shape of both the upstream opening 8u and the downstream opening 8d is a perfect circle, the upstream opening center of gravity 9u and the downstream opening center of gravity 9d coincide with the center of the perfect circular figure. Next, the direction that passes through the upstream opening center of gravity 9u and the downstream opening center of gravity 9d and faces the downstream side is defined as the flow path axial direction 10. In the example shown in FIG. 10, the flow path axial direction 10 is the same direction as the sliding surface vertical downstream direction 32. In FIG. 10F, the line drawn by the alternate long and short dash line is the flow path axial direction 10.

Next, the flow path hole 6 of the sliding gate 1 of the present invention will be described with reference to FIG. The sliding gate 1 of FIG. 2 has three plates, and is composed of an upper fixing plate 3, a slide plate 4, and a lower fixing plate 5 from the upstream side. Each plate is formed with a flow path hole 6 having a cylindrical shape having a perfect circular cross section in the axial direction, and the axial direction of the cylinder is a direction inclined from the vertical downstream direction 32 of the sliding surface. The upper fixing plate 3 will be described as an example with reference to FIGS. 2A and 2F. FIG. 2 (F) is a cross-sectional view taken along the line FF of FIG. 2 (A). Since the axial direction of the cylinder and the vertical downstream direction 32 of the sliding surface are tilted, the upstream opening 8u and the downstream opening 8d are drawn at different positions in FIG. 2A. Since the axial cross section is a perfect circle and the axial direction is a cylindrical shape inclined from the sliding surface perpendicular downstream direction 32, the upstream opening 8u and the downstream opening 8d each form an ellipse slightly deviating from the perfect circle. ing. However, it is drawn as a perfect circle on the drawing for convenience. The centers of gravity of the figures of the upstream opening 8u and the downstream opening 8d can be defined as the upstream opening center of gravity 9u and the downstream opening center of gravity 9d, respectively. Further, the flow path axial direction 10 can be determined so as to pass through the upstream opening center of gravity 9u and the downstream opening center of gravity 9d and face the downstream side. In FIG. 2F, the line drawn by the alternate long and short dash line is the flow path axial direction 10. In the example shown in FIG. 2, the flow path axial direction 10 coincides with the axial direction of a cylindrical shape having a perfect circular cross section forming the flow path hole 6. Here, the angle formed by the downstream direction perpendicular to the sliding surface of the plate (the vertical downstream direction 32 of the sliding surface) and the flow path axis direction 10 is defined as the flow path axis inclination angle α. Here, the reason why the center of gravity of the hole is used instead of the center of the circle to determine the direction of the flow path axis is to universally define the direction of the flow path axis even when the shape of the hole is not a perfect circle.

In the example shown in FIG. 10, the downstream opening 8d of the upper fixing plate 3 and the upstream opening 8u of the slide plate 4 and the downstream opening 8d of the slide plate 4 and the upstream opening 8u of the lower fixing plate 5 coincide with each other. The sliding position of the slide plate 4 is fixed, that is, the sliding gate 1 is in a fully open state (see FIG. 10 (D)). The sliding gate 1 shown in FIG. 10 can reduce the opening degree of the sliding gate 1 by moving the slide plate 4 to the left in the drawing. FIG. 11 shows a state in which the opening degree is halved for the same sliding gate 1 as in FIG. The sliding gate 1 can be fully closed by further moving the position of the slide plate 4 to the left side of the drawing. The same applies to the examples shown in FIGS. 2 and 3. In FIG. 2, the sliding gate 1 is fully opened, and the downstream opening 8d of the upper fixing plate 3 and the upstream opening 8u of the slide plate 4, the downstream opening 8d of the slide plate 4 and the upstream opening 8u of the lower fixing plate 5 are shown. The sliding positions of the slide plate 4 are determined so as to match each other. FIG. 3 shows a state in which the opening degree of the sliding gate 1 is halved with respect to the same sliding gate 1 as in FIG. Therefore, the direction in which the slide plate 4 slides when the sliding gate 1 is closed is hereinafter referred to as "sliding closing direction 33".

In the example of the present invention shown in FIG. 2, since the flow path axis direction 10 is tilted at the flow path axis inclination angle α with respect to the sliding surface vertical downstream direction 32, the flow path axis direction 10 is projected onto the sliding surface. When the direction is the sliding surface flow path axial direction 31, the sliding surface flow path axial direction 31 can be determined. The sliding surface flow path axial direction 31 is indicated by a thin arrow in each of FIGS. 2 (A) to 2 (C) and (F). In FIGS. 2A to 2C, the sliding surface flow path axial direction 31 overlaps with the flow path axial direction 10. Further, in the example shown in FIG. 10, since the flow path axial direction 10 faces the sliding surface vertical downstream direction 32, the sliding surface flow path axial direction 31 does not appear in FIGS. 10A to 10C. ..

Next, the angular relationship between the sliding surface flow path axial direction 31 and the sliding closing direction 33 is defined. The angle formed by the sliding surface flow path axis direction 31 clockwise with respect to the sliding closing direction 33 in the sliding surface perpendicular downstream direction 32 is called a flow path axis rotation angle θ. The flow path axis rotation angle θ is defined as an angle in the range of ± 180 °. That is, when the sliding surface flow path axial direction 31 becomes an angle (θ') that exceeds + 180 ° clockwise when viewed in the sliding surface vertical downstream direction 32, it is set as "θ = θ'-360 °". The angle θ is defined as a negative value. As subscripts of the angle θ, the θ of the most upstream plate is numbered θ ₁ , the θ of the plate one downstream of it is θ ₂ , and the θ of the plate one downstream is θ ₃ . When expressed as θ _N as a representative, N is an integer of 1 or more and means a numerical value up to the number of plates of the sliding gate 1. In the example shown in FIG. 2, the upper fixing plate 3 has an angle θ ₁ = −45 °, the slide plate 4 has an angle θ ₂ = + 90 °, and the lower fixing plate 5 has an angle θ ₃ = −135 °.

Further, in the sliding gate 1, the relationship between the flow path axis rotation angles between the two plates in contact with each other is defined as follows. That is, defining the _{Δθ N = θ N -θ N +} 1 as a [Delta] [theta] _N. Δθ _N is defined as an angle in the range of ± 180 degrees, similar to θ _N above. That is, the angle ([Delta] [theta] _N ') in which [Delta] [theta] _N is greater than + 180 ° when a is "Δθ _N = Δθ _N' as -360 °", defining the [Delta] [theta] _N as a minus value. When Δθ _N becomes an angle less than −180 ° (Δθ _N ′), Δθ _N is defined as a positive value as “Δθ _N = Δθ _N ′ + 360 °”. As a result, Δθ _N becomes a number within the range of ± 180 °. Here, when Δθ _N is more than 0 ° and less than + 180 °, it indicates that the flow path axis rotation angle θ _N changes counterclockwise from upstream to downstream. On the contrary, when Δθ _N is more than −180 ° and less than 0 °, it indicates that the flow path axis rotation angle θ _N changes clockwise from the upstream to the downstream. In the example shown in FIG. 2, the _{Δθ 1 = θ 1 -θ 2 =} -135 °, Δθ 2 '= θ 2 -θ 3 = 225 since it is _{° Δθ 2 = Δθ 2' -360} ° = -135 ° .. Since both Δθ ₁ and Δθ ₂ are in the range of −180 to 0 °, it indicates that the flow path axis rotation angle changes clockwise.

Based on the above preparations, the conditions to be satisfied by the sliding gate 1 of the present invention and the reasons thereof will be described.

In the conventional sliding gate 1, as shown in FIGS. 10 and 11, the flow path axis direction 10 is perpendicular to the sliding surface, that is, the flow path axis inclination angle α is 0 ° and has an inclination. There wasn't. On the other hand, the first feature of the present invention is that the flow path axis direction 10 is inclined with respect to the sliding surface perpendicular downstream direction 32, and the flow path axis inclination angle α is not 0 °. Since the flow path axis is tilted with respect to the sliding surface vertical downstream direction 32, the molten metal flowing in the plate is not only the velocity component in the sliding surface vertical downstream direction 32 but also in the sliding surface vertical downstream direction 32. On the other hand, it has a velocity component (horizontal velocity component) at right angles. In the present invention, the flow path axis inclination angle α is 5 ° or more and 75 ° or less. By setting the angle α to 5 ° or more, the molten metal has a sufficient velocity component in the horizontal direction, and as shown below, it is possible to form a swirling flow in the immersion nozzle. The angle α is preferably 15 ° or more, more preferably 25 ° or more. On the other hand, if the angle α is too large, it is not preferable from the viewpoint of ensuring the strength of the refractory and suppressing wear, so the angle α is set to 75 ° or less. The angle α is preferably 65 ° or less, more preferably 55 ° or less.

Regarding the opening state of the sliding gate 1 during continuous casting, the opening of the sliding gate is fully opened (see FIG. 10) in a steady state where the molten metal level in the tundish is constant and casting is performed at a constant casting speed. Instead, the cross-sectional area of the sliding gate flow path hole is selected so that casting can be performed in a state where the opening degree is narrowed (see FIG. 11). In FIG. 11, the opening degree of the sliding gate 1 is 1/2. In this case, the opening area of the sliding gate 1 is calculated to be 0.31 times the cross-sectional area of the flow path hole which is a perfect circle. As a result of the small cross section narrowed in this way becoming the opening area during steady continuous casting, a high-speed flow of the small cross section flows in the flow path on the downstream side of the slide plate 4 of the sliding gate 1. It becomes a situation.

FIG. 3 shows a sliding gate having the shape shown in FIG. 2 when the opening degree of the sliding gate 1 (opening fully open) of the present invention is changed to halve the opening degree. FIG. 3A is a view taken along the line AA of FIG. 3D, in which the downstream opening 8d of the upper fixing plate 3 is partially drawn with a solid line and a part with a broken line, and the slide plate 4 is upstream. Only the opening 8u (4) is also drawn with a solid line and a broken line. FIG. 3B is a view taken along the line BB of FIG. 3D, in which the upstream opening 8u of the slide plate 4 is entirely drawn with a solid line, the downstream opening 8d is partially drawn with a solid line, and partly with a broken line. The upstream opening 8u of the lower fixing plate 5 is also drawn with a solid line and a part with a broken line, and the downstream opening 8d is drawn with a broken line. FIG. 3C is a view taken along the line CC of FIG. 3D, in which the upstream opening 8u of the lower fixing plate 5 is drawn with a solid line, the downstream opening 8d is drawn with a solid line, and a broken line. There is.

The flow of molten metal in the flow path hole of the sliding gate and in the immersion nozzle when the opening degree is halved as shown in FIG. 3 will be described with reference to FIG. In FIG. 4, FIG. 4 (A) is a view taken along the line AA of FIG. 4 (D), in which the downstream opening 8d of the upper fixing plate 3 is partially drawn with a solid line and a part with a broken line, and is a slide plate. For No. 4, only the upstream opening 8u is also drawn with a solid line and a broken line. FIG. 4B is a view taken along the line BB of FIG. 4D, in which the position of the downstream opening 8d (3) of the upper fixing plate 3 is indicated by a chain double-dashed line, and the upstream opening of the slide plate 4 is shown. 8u is all solid line, downstream opening 8d is partially solid line, partly broken line, upstream opening hole 8u of the lower fixing plate 5 is also partly solid line, partly broken line, downstream opening 8d is all broken line It is drawn in. FIG. 4C is a view taken along the line CC of FIG. 4D, in which the position of the downstream opening 8d (4) of the slide plate 4 is indicated by a chain double-dashed line, and the upstream opening of the lower fixing plate 5 is shown. All 8u are drawn with solid lines, and the downstream opening 8d is drawn with some solid lines and some broken lines. The streamline 18 of the molten metal is indicated by a thick arrow in FIGS. 4 (A) to 4 (C) and a thick dashed arrow in (D) and (E).

2, the sliding gate 1 of FIG. 3, as described above, the difference [Delta] [theta] _N of adjacent flow channel axis rotation angle theta _N is a _{Δθ 1 = Δθ 2 = -135 °} , both [Delta] [theta] _N is Since it is more than −180 ° and less than 0 °, it indicates that the flow path axis rotation angle θ _N changes clockwise from the upstream to the downstream. As shown in FIG. 4A, the molten metal flow flowing through the flow path hole 6 of the upper fixing plate 3 flows along the flow path axial direction 10 of the upper fixing plate 3. On the contact surface between the upper fixing plate 3 and the slide plate 4, the downstream opening 8d of the upper fixing plate 3 (two-dot chain line in FIG. 4B) and the upstream opening 8u of the slide plate 4 (solid line in FIG. 4B). ) Flows down in the small cross section of the overlapping portion (opening). In the flow path hole 6 of the slide plate 4, the downstream opening 8d of the upper fixing plate 3 (two-dot chain line in FIG. 4B) and the upstream opening 8u of the slide plate 4 (solid line in FIG. 4B). The molten metal flow flowing out from the small cross section of the overlapping portion (opening) with the slide plate 4 is along the inner wall surface (cylindrical surface) of the flow path hole 6 of the slide plate 4, as shown by the streamline 18 in FIG. 4 (B). The swirling flow is formed, and the downstream opening 8d of the slide plate 4 (two-dot chain line in FIG. 4C) and the upstream opening 8u of the lower fixing plate 5 (solid line in FIG. 4C) are formed on the downstream side. Further flows out from the small cross section of the overlapping portion (opening) into the flow path hole 6 of the lower fixing plate 5. In the flow path hole 6 of the lower fixing plate 5, a swirling flow is formed along the inner wall surface (cylindrical surface) of the flow path hole 6 of the lower fixing plate 5 as shown by the streamline 18 in FIG. 4 (C). As it is, it flows out into the immersion nozzle 11 on the downstream side, and as shown in FIGS. 4D and 4E, the streamline 18 keeps the swirling flow in the flow path and moves the inside of the immersion nozzle 11 to the downstream side. I will move.

When the conventional sliding gate 1 as shown in FIG. 11 is used, all of the kinetic energy of the molten metal flow when flowing out from the opening of the sliding gate 1 is consumed by the flow velocity in the downstream direction. There is. On the other hand, when the sliding gate 1 of the present invention as shown in FIG. 3 is used, when the sliding gate 1 flows out, the kinetic energy of the molten metal flow swirls with the flow velocity in the downstream direction and is inside the immersion nozzle. Since it is dispersed in the turning speed of turning on the peripheral surface, it is possible to suppress the flow velocity in the downstream direction as compared with the conventional sliding gate 1 shown in FIG.

The difference between the flow path axis rotation angles θ _{N of} adjacent plates for forming a swirling flow in the flow path hole 6 of the sliding gate 1 and forming a swirling flow in the immersion nozzle on the downstream side of the sliding gate. The condition of a certain angle Δθ _N will be described. As mentioned above, Δθ _N is defined as an angle within the range of ± 180 °. Here, when Δθ _N = more than −10 ° and less than + 10 °, the difference between the flow path axis rotation angles θ _N and θ _{N + 1} is too small to form a swirling flow. On the other hand, when Δθ _N is + 170 ° or more or −170 ° or less, the absolute value of Δθ _N is too large, which rather hinders the formation of a swirling flow. When the sliding gate 1 has two plates, only Δθ ₁ is defined, and it is sufficient that the Δθ ₁ satisfies the above condition. When the sliding gate 1 has three or more plates, in addition to Δθ ₁ , Δθ ₂ and even more Δθ _N are defined. Then, it is necessary that both Δθ _N are 10 ° or more and less than 170 °, or the angles Δθ _N are both more than −170 ° and less than −10 °. As a result, when the flow path axial direction 10 of the first and second plates changes clockwise, the third and subsequent plates also change clockwise in the same manner, and the first and second plates also change clockwise. When the flow path axial direction 10 changes counterclockwise, the third and subsequent sheets also change counterclockwise in the same manner, so that a swirling flow can be effectively formed in the sliding gate. A more preferable range of Δθ _N is 30 ° or more and less than 165 °, or more than -165 ° and −30 ° or less.

The number of plates forming the sliding gate 1 is preferably two or three. In the examples shown in FIGS. 2 to 4, as described above, the number of plates is three. In FIGS. 5 and 6, the number of plates is two, and the first plate from the upstream side constitutes the upper fixing plate 3 and the second plate constitutes the slide plate 4. FIG. 5 shows a case where the opening degree is fully opened, and FIG. 6 shows a case where the opening degree is 1/2. α = 51.95 °, θ ₁ = −26.57 °, θ ₂ = + 26.57 °, and Δθ ₁ = −53.14 °, and a clockwise swirling flow can be formed. The reason why it is preferable that the number of plates forming the sliding gate 1 is two or three is that at least two plates are required to express the drawing mechanism of the sliding gate, and four or more plates are not required for flow rate adjustment. This is because the cost increases as the number of plates increases.

The flow path hole 6 formed in the plate may be a flow path hole 6 having a shape as shown in FIG. 7. FIG. 7 shows an example of the upper fixing plate 3. From the upstream surface 7u of the plate to the middle of the thickness, the shape of the flow path hole 6 is a cylindrical shape with a perfect circular cross section, and the axis of the cylinder faces the sliding surface perpendicular downstream direction 32. From the downstream surface 7d of the plate to the middle of the thickness, the shape of the flow path hole 6 is a cylindrical shape with a perfect circular cross section, and the axis of the cylinder is formed so as to be inclined from the vertical downstream direction 32 of the sliding surface. In the middle of the thickness of the plate, the flow path hole 6 from the upstream surface 7u and the flow path hole 6 from the downstream surface 7d are connected without a step. Even in a plate having a flow path hole 6 having such a shape, as shown in FIG. 7D, the center of gravity of the upstream surface opening figure (upstream opening center of gravity 9u) to the center of gravity of the downstream surface opening figure ( The direction toward the downstream opening center of gravity 9d) can be defined as the flow path axial direction 10.

The thickness of the plates constituting the sliding gate 1 may be the same, but the thickness may be different for each plate such that the slide plate 4 is the thinnest. Further, the shape of the flow path holes at the inlet and outlet of each plate of the sliding gate may be a circle of the same size, but even if this is an ellipse or an oval, a swirling flow can be obtained as long as the provisions of the present invention are satisfied. Is possible. Alternatively, the opening area may be different at the inlet and outlet of each plate.

The angle α may be the same or different for all plates.

《Water model experiment》
In order to quantitatively evaluate the horizontal component of the discharge flow during continuous casting, the velocity distribution near the discharge hole was measured by the particle image flow velocity measurement method using a 1/1 scale water model experimental device. In particular, when the inner diameter of the gate was set to D, attention was paid to the velocity distribution at a position 1.0D from the tip of the discharge hole, and the average of the horizontal velocity components at that position was defined as "horizontal velocity strength". Here, the 1/1 scale water model experiment of continuous casting sufficiently reproduces the molten steel flow from the viewpoint that the Froude number Fr and the Reynolds number Re match.

As the sliding gate, a sliding gate of the present invention (hereinafter referred to as "the gate of the present invention") that forms a swirling flow in the immersion nozzle and a conventional sliding gate (hereinafter referred to as "normal gate") Prepared. In both the gate of the present invention and the normal gate, the plate thickness is 35 mm, and the flow path hole diameter of the plate is φ50 mm. Here, the flow path hole matches the diameter of the drill used to drill the plate.

Regarding the flow path axis inclination angle α formed by the downstream direction perpendicular to the sliding surface 30 of the plate 2 (sliding surface vertical downstream direction 32) and the flow path axis direction 10, the α of the upper fixing plate 3 is α ₁ and slides. The α of the plate 4 is numbered α ₂ , and the α of the lower fixing plate 5 is numbered α ₃ . Similarly, the upper fixing plate 3, the slide plate 4, and the lower fixing plate 5 also have a flow path axis rotation angle θ which is an angle formed by the sliding surface flow path axis direction 31 clockwise when viewed in the sliding surface vertical downstream direction 32. Each θ is numbered in the order of θ ₁ , θ ₂ , and θ ₃ .

The gate of the present invention has the shapes shown in FIGS. 2 to 4, α ₁ = α ₃ = 35.531 °, α ₂ = 32 °, θ ₁ = 36.101 °, θ ₂ = 90 °, θ ₃ = 143.899 ° (36.101-180), and a clockwise swirling flow is formed in the molten steel flow flowing down into the inner hole of the immersion nozzle. The normal gate has the shapes shown in FIGS. 10 and 11, α ₁ = α ₂ = α ₃ = 0 °, and θ ₁ , θ ₂ , and θ ₃ have no values.

As the immersion nozzle 11, a single-hole immersion nozzle in which the discharge hole 13 is opened downward at the bottom of the immersion nozzle was used. As the shape of the discharge hole 13, three types shown in FIG. 12 were used. In FIG. 12A, the discharge hole 13 is a straight pipe. 12 (B) and 12 (C) have a tubular shape extending from the inner wall of the immersion nozzle toward the outlet of the discharge hole. FIG. 12B is a mountain shape in which the discharge hole 13 expands linearly, and FIG. 12C is a trumpet type in which the discharge hole 13 smoothly opens from the inner wall in a curved line. Further, the straight tube single-hole immersion nozzle includes a normal straight-tube single-hole immersion nozzle having a simple cylindrical inner wall shape above the immersion nozzle and a blade having the blades shown in Patent Document 1 formed above the immersion nozzle. Two types of straight pipe single-hole immersion nozzles were prepared.

For the sliding gate and the immersion nozzle, the combinations shown in Table 1 were prepared, and water model experiments were conducted for each.

For each of the test condition C (example of the present invention) and the test condition E (comparative example) in Table 1, the flow velocity and the flow direction of the discharge flow 19 on the downstream side of the discharge hole 13 were measured. The inner diameter of the discharge hole is D (= 50 mm), the flow velocity and the flow direction are measured at the outlet of the discharge hole, 1.0D below the discharge hole, and 2.0D below the discharge hole, and a schematic diagram of the result is shown in FIG. Indicated. FIG. 13 (A) shows the test condition C (example of the present invention), and FIG. 13 (B) shows the test condition E (comparative example). As shown in FIG. 13, when a normal gate is used and no swirling flow is applied, the discharge flow 19 below the discharge hole 13 does not have a horizontal flow velocity component, and the flow path as it goes downward The spread is also slight. On the other hand, in the case of the present invention provided with a swirling flow, the discharge flow 19 below the discharge hole 13 has a flow velocity component in the horizontal direction, and the spread of the flow path increases as it goes downward. It became clear.

Further, for all the test conditions A to E in Table 1, the measurement results of the horizontal velocity component strength and the casting direction velocity component strength are shown in the same Table 1.
First, in the case where the outlet shape of the discharge hole of the single-hole immersion nozzle is a straight pipe, the effect of the combination of the sliding gate (hereinafter, also simply referred to as “gate”) and the internal structure of the immersion nozzle upper part on the swirling flow was evaluated. As is clear from Table 1, the internal structure of the upper part of the immersion nozzle is a normal cylindrical structure, and in combination with the normal gate (test condition E), a large discharge flow rate is shown in the casting direction, but the internal structure of the upper part of the immersion nozzle has blades. It can be seen that the velocity of the fluid flowing in the casting direction is reduced in the combination of the normal gate (test condition D) and the combination of the gate of the present invention and the cylindrical structure in which the upper internal structure of the immersion nozzle is normal (test condition C). .. This is because the internal structure of the upper part of the immersion nozzle is a normal cylindrical structure, and the horizontal velocity that did not occur in combination with the normal gate (test condition E) generates a swirling flow in the immersion nozzle. It is considered that this is because the structure was added by the combination of the usual cylindrical structure (test condition C).
Next, using the gate of the present invention as the sliding gate, the influence of the outlet shape of the discharge hole of the single-hole immersion nozzle was evaluated. Focusing on the outlet shape of the discharge hole of the single-hole immersion nozzle, even if the outlet shape is a straight pipe shape (test condition C), the casting direction speed is suppressed by the effect of turning, and the horizontal speed is added. On the other hand, if the outlet shape of the discharge hole is a trumpet shape (test condition A) or a chevron shape (test condition B), the effect of suppressing the speed in the casting direction is larger than that of the straight pipe shape (test condition C) and the horizontal shape. The effect of increasing the directional speed was clarified. It is considered that this is because the Coanda effect is exhibited in which the fluid flowing in the casting direction is attracted to the trumpet-shaped or chevron-shaped wall in the horizontal direction due to the viscosity near the wall.

The present invention was applied to a bloom continuous casting apparatus (2 strands) having a ladle molten steel amount of 200 tons. The shape of the slab to be cast is width: 250 mm and thickness: 250 mm. The tundish capacity is 35 tons, and a hot water pouring device for continuous casting is provided at the bottom of the tundish. The pouring device for continuous casting has a sliding gate for adjusting the flow rate of the molten metal, and a dipping nozzle provided below the sliding gate. The sliding gate has three plates in which a flow path hole through which the molten metal passes is formed, and the central plate is a slidable slide plate. The immersion nozzle is a single-hole immersion nozzle.

As the sliding gate, the gate of the present invention similar to the water model experiment, the normal gate, was used. Further, as the immersion nozzle, the same nozzle as in the water model experiment was used.

As a method for evaluating the skin tension of the molten metal due to the decrease in the temperature of the molten metal, the occurrence rate of powder entrainment defects in the slab after casting is taken up. The occurrence rate of powder entrainment defects in the slab was evaluated as the occurrence rate of powder-induced defects found at the product stage. Based on the condition (test condition E) where a normal gate is used as the sliding gate of the pouring device for continuous casting and a normal nozzle is used as the immersion nozzle, the occurrence rate of powder entrainment defects is used as a reference (1.0), and the powder under each condition is used. The incidence of entanglement defects was indexed and used as "slab quality".

The durability of the continuous casting pouring device was evaluated based on the longest casting time (hereinafter referred to as "non-replacement casting time") in which the refractory material of the continuous casting pouring device can be used without replacement. Casting time without replacement under the condition (test condition E) where a normal gate is used as the sliding gate of the pouring device for continuous casting and a normal nozzle is used as the immersion nozzle is used as a reference (1.0), and the casting time without replacement under each condition. Was indexed and used as the "durability index".

Table 2 shows the conditions of the sliding gate and immersion nozzle used as the pouring device for continuous casting, and the casting results.

From Table 2, it is estimated that the nozzle with blades (test condition D) and the gate of the present invention (test conditions A to C), which generate swirl in the hot water supply flow to the mold, improved the slab quality and reduced the surface coating of the hot water in the mold. it can. Further, it can be seen that when the outlet shape of the immersion nozzle is a chevron shape (test condition B) or a trumpet shape (test condition A), the slab quality is further improved. This is consistent with the tendency that the horizontal velocity component strength shows a larger value when the outlet shape of the discharge hole of the single-hole immersion nozzle is a mountain shape or a trumpet shape as shown in Table 1. That is, it is suggested that if the outlet shape of the discharge hole is a chevron shape or a trumpet shape, the amount of heat supplied to the hot water surface in the mold is increased and the skin on the hot water surface in the mold is prevented. Further, regarding the refractory durability, the gate of the present invention (test conditions A to C) showed a higher value than the nozzle with blades (test condition D), which showed the lowest value. Furthermore, it was also clarified that the refractory durability index of the gates of the present invention (test conditions A to C) was 1.3, which was higher than that of the normal gate under test condition E.

1 Sliding gate 2 Plate 3 Upper fixing plate 4 Sliding plate 5 Lower fixing plate 6 Flow path hole 7u Upstream surface (upstream side surface)
7d Downstream surface (downstream side surface)
8u upstream opening (upstream surface opening)
8d Downstream opening (downstream surface opening)
9u upstream opening center of gravity (upstream surface opening graphic center of gravity)
9d Center of gravity of downstream opening (center of gravity of downstream surface trench drawing)
10 Flow path axial direction 11 Immersion nozzle 12 Immersion nozzle Inner hole 13 Discharge hole 18 Stream line 19 Discharge flow 20 Hot water pouring device for continuous casting 21 Tundish 22 Mold 23 Molten metal 30 Sliding surface 31 Sliding surface Flow path axial direction 32 Sliding surface vertical downstream direction 33 Sliding closed direction α Flow path axis tilt angle θ Flow path axis rotation angle

Claims (3)

A pouring device for continuous casting for pouring molten metal into a mold.
It has a sliding gate for adjusting the flow rate of the molten metal and a dipping nozzle provided below the sliding gate.
The sliding gate has a plurality of plates having flow path holes through which molten metal passes, and at least one of the plates is a slidable slide plate.
The flow path holes in each plate form an upstream surface opening on the upstream surface located on the upstream side of the molten metal passing through the surface of the plate, and a downstream surface on the downstream surface located on the downstream side. A hole is formed, and the direction from the center of gravity of the upstream surface opening figure to the center of gravity of the downstream surface opening figure is defined as the flow path axis direction.
The flow path axis inclination angle α formed by the downstream direction perpendicular to the sliding surface of the plate (hereinafter referred to as “sliding surface vertical downstream direction”) and the flow path axis direction is 5 ° or more and 75 ° or less.
The direction in which the flow path axis direction is projected onto the sliding surface is called the sliding surface flow path axis direction, and the direction in which the slide plate is slid when the sliding gate is closed is called the sliding closing direction. The angle formed by the sliding surface flow path axis direction clockwise with respect to the closing direction when viewed in the direction perpendicular to and downstream of the sliding surface is called the flow path axis rotation angle θ (range of ± 180 degrees), and the flow path is said to be The axis rotation angle θ differs between adjacent plates, with θ ₁ for the most upstream plate, θ _{2 for} the one downstream plate, and θ for the one downstream plate θ. _When numbered in order of ₃ and Δθ _N = θ _N −θ _{N + 1} (N is an integer of 1 or more and the number of plates is -1)
Both angles Δθ _N are greater than or equal to 10 ° and less than 170 ° to form a counterclockwise swirling flow in the immersion nozzle, or angles Δθ _N are both greater than −170 ° and less than −10 ° and the immersion nozzle. Forming a clockwise swirling flow inside,
The immersion nozzle is a hot water pouring device for continuous casting, characterized in that it has a single discharge hole opened at the bottom of the immersion nozzle. The water pouring device for continuous casting according to claim 1, wherein the discharge hole shape of the immersion nozzle is formed so as to have an expanded tubular shape from the inner wall of the immersion nozzle toward the discharge hole outlet. The pouring device for continuous casting according to claim 1 or 2, wherein the number of plates forming the sliding gate is two or three, and the number of slide plates is one.

Images